A Binol‐Strapped Calix[4]pyrrole as a Model Chirogenic Receptor for the Enantioselective Recognition of Carboxylate Anions

Abstract

Binding straps: Chiral calix[4]pyrroles 1 bearing an (R)‐ or (S)‐binol‐derived strap on one side of the tetrapyrrolic core (see picture) were synthesized and characterized. The resulting systems bind selected chiral carboxylate anions (shown in red) with high affinity in acetonitrile while at the same time exhibiting enantiomeric discrimination. PB=2‐phenylbutyrate.

Syntheses of Calix[4]Pyrroles by Amberlyst-15 Catalyzed Cyclocondensations of Pyrrole with Selected Ketones

“…The reactions of pyrrole with dialkyl ketones in the presence of protic acids (HCl, H 2 SO 4 ), organic acids (CH 3 SO 3 H) and Lewis acids (BBr 3 and BF 3 ) have also been used in the synthesis of calix [4]pyrroles [29][30][31][32][33]. The reaction of excess of pyrrole with dialkylketones in the presence of acid gave 5,5-dialkyldipyrromethanes which on subsequent reaction with dialkylketones in the presence of borontrifluoride-etherate formed strapped calix [4]pyrroles [34,35]. These acids are considered hazardous and corrosive and their removal from the reaction mixtures is difficult.…”

Recent progress on using BINOLs in enantioselective molecular recognition

“…This pep interaction likely causes the energy difference between these two diastereomers, and explains the chiral recognition ability of (S)-88. 97 6.1.2. Enantioselective extraction.…”

Calix[n]pyrroles as Anion and Ion-Pair Complexants

“…Such systems would be potentially useful in the recognition and, potentially, separation of various anion-containing enantiomeric species, including amino acids. With these regards, a pair of chiral calix [4]pyrroles, (S)-52 and (R)-52, was prepared [71].…”